So I understand the basic principles behind noise cancellation. You essentially use a microphone to record incoming sound waves and create an inverse wave that destructively interferes with the initial wave, thus, cancelling it out. But I don’t understand, practically, how this is done.
Let’s assume the sound wave makes contact with the microphone in the AirPod, which analyses the wave and shoots out an inverse wave, but by that point – the initial sound wave would surely have already reached my ears. The AirPod basically needs to cancel the sound wave before it moves roughly a centimetre or it’s too late.
The speed of sound (in a standard environment like air) is 343 meters per second or 34,300 centimetres per second; this means the AirPod has 1/34,300 seconds or ~0.03 miliseconds to do these operations to cancel the wave. That just seems absurd to me for such a tiny chip in the bloody AirPod.
Someone fix my confusion please.
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As someone already mentioned, today’s microcontrollers are “wicked fast”. Yet, they’re not the fastest! Because, you see, they’re actually “general purpose” computers and, as such’ have to do many things that may or may not be related to a particular task (in this case, noise cancellation).
Some “computers” are built specifically to deal with processing fast signals, and these are called Digital Signal Processors (DSPs). These are way faster at their job than normal processors (but not much good at anything else).
Also, FPGAs (or Field-Programmabla Gate Arrays) are nothing more than the very basic building blocks of microcontrollers, except they are not pre-configured in any general purpose functions, but instead are left for the developer to arrange them in the best way to efficiently solve the task at hand. This is more complicated to do, but the end result is MUCH faster than a run-of-the-mill controller.
If there is enough of a market (and hundreds of thousands of headsets should be), then engineers design special-purpose chips FROM SCRATCH that do one thing and one thing only (and nothing else), but in the most effective way. These are called, for obvious reasons, Application-Specific Integrated Circuits or ASICs. Let’s just say that they are fast…
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